1. Field of the Invention
The present invention relates to silicon carbide single-crystals and in particular to silicon carbide single-crystals produced by supplying superfine silicon dioxide particles and superfine carbon particles to nucleating silicon carbide crystals and reducing the silicon dioxide by the carbon.
2. Description of the Prior Art
Silicon carbide single-crystals are useful as materials for semiconductor devices such as environmental-resistant devices, power devices etc., and for producing them, various processes are used. Generally, the liquid phase of silicon carbide is not present at normal pressures and the crystallization thereof from the liquid phase is difficult by methods such as a drawing method for silicon single-crystals, and thus silicon carbide is produced conventionally by a process of sublimation i.e. crystallization from gaseous phases such as Si2C, SiC2 and Si. The process of sublimation includes an Acheson process for producing silicon carbide single-crystals by heating silicic anhydride and a carbon source at high temperatures and subsequent reaction thereof in a generated vapor or by a Larry [phonetic transcription] process or a modified Larry process of sublimation of silicon carbide powder in a graphite crucible to re-crystallize silicon carbide single-crystals in the graphite crucible. However, the Acheson process has the problem that the size of the resulting single crystals is low, their purity is low for use in semiconductor devices, while the Larry process and the modified Larry process have the problem that the reaction is complicated because silicon carbide gas does not possess a stoichiometric composition. Further, because its crystals grow while forming each layer from the gaseous phase by supplying atoms and molecules to the surface of nucleating crystals, growth of the single crystals in any of these processes is as significantly slow as about 1 mm/hour, as compared with a growth rate of about 100 mm/hour achieved by the drawing process for silicon single-crystals, and the yield in the prior art processes is also low. Further, the deficiency of hollows of several microns in diameter such as micro-pipes occurs easily, and xcex2-type crystals are hardly obtained in the prior art processes.
As the method of crystallization from the gaseous phase, there is also a CVD method, but the resulting crystals are a thin film hardly usable as single crystals in substrates for devices etc.
The object of the present invention is to provide silicon carbide single-crystals of high-purity and large diameters obtainable at a higher rate of crystalline growth at lower costs with less generation of micro-pipes.
That is, the present invention relates to silicon carbide single-crystals comprising silicon carbide single-crystals grown on nucleating silicon carbide crystals, which are prepared by supplying and sticking superfine silicon dioxide particles and superfine carbon particles onto the surface of nucleating silicon carbide crystals kept in a heated state in an inert gas atmosphere and reducing the silicon dioxide by the carbon on the surface of the nucleating silicon carbide crystals thereby allowing silicon carbide single-crystals to grow on the nucleating silicon carbide crystals.
In the present invention, superfine silicon dioxide particles are heated at high temperatures, allowed to adhere to the surface of nucleating silicon carbide crystals, melted, fused into superfine carbon particles and reduced on the surface of said nucleating crystals, to form fine silicon carbide crystals, and by the phenomenon of melting and fluidization of the superfine particles, the formed fine silicon carbide crystals are fused into the surface of the nucleating crystals and formed into epitaxial crystals as single-crystals. The silicon carbide single-crystals of the present invention are obtained by directly supplying solid silicon dioxide and carbon to the surface of nucleating crystals and reacting them on the surface of the nucleating crystals, so that the rate of growth of single-crystals is rapid and micro-pipes occur hardly.